Alkylation of aromatic compounds



Patented Jan. 29, 1946 UNITED STATES PATENT orrlcs 2,393,818 ALKYLATION OF AROMATIC COMPOUNDS Louis Schmerling, Chicago, 111., neither to Uni- Products Company, Chicago, 111., a

corporation of Delaware No Drawing. Application September 28, 1942, Serial No. 459,949

Claims. (Cl. 260-871) aromatic hydrocarbons which comprises react-' ing an aromatic hydrocarbon with an oleflnic hydrocarbon under alkylating conditions in the presence of a solution formed by adding an aluminum halide and a catalytically inert salt to a nitroparaflin.

Mono nuclear aromatic hydrocarbons such as benzene, toluene, and other alkylated benzenes as well as the ;.po1y nuclear aromatics including naphthalene and the alkylated naphthalenes may be alkylated in accordance with the present process as hereinafter described in greater detail.. These aromatic hydrocarbons are readily available as by-products in the coal tar industry and they may be obtained by the dehydrogenation of naphthanic hydrocarbons, by the dehydrogenation and cyclization of aliphatic hydrocarbons and by other means.

Either normally gaseous or normally liquid oleflns including ethylene, propylene, butylenes and the higher homologues thereof may be employed as alkylating agents. Polymers, dioleflns, cyclic oleflns and other poly oleilns may also be reacted with aromatic hydrocarbons but not necessarily under the same conditons of operation which may be employed when aromatic hydrocarbons are alkylated with the straightchain and branched chain oleflns. The allphatic olefins are generally available from the catalytic or thermal cracking of hydrocarbon oils and also from various other hydrocarbon conversion reactions. In certain cases various olefin-producing substances such as alcohols, ethers, esters, alkyl halides, etc. may be utilized as alkylating agents to produce alkyl aromatics, although again the olefin-producing substances are not to be considered as being on an equivalent basis with other alkylating agents since somewhat different operating conditions may be necessary.

A solution formed by adding an aluminum halide such as aluminum chloride, aluminum such as nitromethane, nitroethane, l-nitropropane, z-nitropropane or a nitroparamn or higher molecular weight is an efiective catalyst for the alkylation of aromatic hydrocarbons with the various alkylating agents hereinbefore described. Under ordinary alkaylating conditions of temperature and pressure such solutions of aluminum chloride are frequently miscible with the aromatic hydrocarbon, e. g., benzene, which is undergoing alkylation. In a certain sense the 'nitroparaflin may thus be said to serve as a solutizer for distributing the aluminum chloride in the aromatic hydrocarbon phase. Thus if one part by weight of aluminum chloride is dissolved in an equal weight of nitromethane and the solution is added to benzene, a clear yellow solution results when either 1 or 100 parts by weight of ducing an alkylating agent into the solution under appropriate conditions.

Whilethe catalytic alkylation of aromatics in a homogeneous system has obvious advantages because of the intimacy of contact between the catalyst and reactants and is of considerable theoretical interest, in most cases it has the practical disadvantage that recycling of the catalyst is not possible since it is dissolved in the single phase product. I have now found that this disadvantage may be overcome to a large extent by employing as a catalyst a solution formed by adding a substantially catalytically inert salt as well as the aluminum halide to a nitroparaflin. In general, I prefer to employ the alkali and alkaline earth halides, particularly 'the chlorides and bromides. The presence of these catalytically inert salts in suflicient amounts minimizes or in many cases prevents the solution 01 the catalyst in the benzene or other aromatic. For ex- .ample, 5 parts by weight of aluminum chloride may be added to 11.3 parts byweight of nitromethane along with 2.2 parts by weight of sodium chloride. A clear yellow solution isobtained which when added to parts by weight of benzene causes the separation of a deep red lower layer. It is apparent that the presence of sodium chloride serves to salt out" the catalyst solution. In general, the alkali and alkaline earth chlorides and bromides are insoluble in/the nitroparaflins but are quite soluble in nitroparaflin solutions of aluminum halides, particularly aluminum chloride.

The difl'erent nitroparaflins which may be used bromide or mixtures thereof to a nitro-paraflin N for forming the catalyst solutions of the present invention do not necessarily produce catalysts which are equivalent in their activity. The particular nitroparaflln chosen will be dependent upon the nature and proportions of the hydrocarbons being reacted, the conditions of opera-' tion, and other factors. The molar ratio of catalytically inert salt to aluminum halide which may'be employed may vary from about 0.1 to about 1.5 or somewhat higher, dependent upon the solubility. In many cases I prefer to have approximately equimolar proportions-of the catalytically inert-salt and the aluminum halide. For example, in the case of sodium chloride, slightly less than 1 .mol of the sodium salt dissolves in the nitropa'raflin for each mol of alu-- minum chloride present.

When aluminum chloride, in the form of a granular solid material, is employed as a catalyst for the alkylation of aromatic hydrocarbons with olefinic hydrocarbons? the formation of sludge-like material upon the surface of the aluminum chloride during use decreases its catalytic activity and ordinarily makes it necessary to withdraw the sludge-like material and replace it with additional quantities of fresh catalyst. A

distinct advantage, however, of the present catalyst which may comprise, for example, nitromethane containing aluminum chloride and sodium chloride, is that only very small quantities of the aromatic reactant are converted to the sludge-like material or lower layer. Therefore, appreciably higher yields are obtained and the catalyst lif is longer. Furthermore, since the catalysts of the present invention are immiscible to a large extent with the hydrocarbon reactants, a separation may readily be effectedbei' ing controlled amounts of the olefinic reactants or other alkylating agent to the reaction zone. The reaction mixture is allowed to settle into an upper hydrocarbon layer which is fractionated for the recovery of desired products of the reaction and unconverted reactants which are recycled to the alkylation zone while a lower used catalyst layer is also withdrawn and may be re-. cycled to the alkylation zone if desired. A portion of the spent catalyst may be continuously or intermittently withdrawn from the system and subjected to hydrolysis for the removal of remaining amounts of aluminum chloride and the nitroparaflins may be separated from the residual mixture by fractional distillation, by extraction or by hydrolysis with a mineral acid. The recovered nitroparaflln may be recycled to further use in the process.

The alkylation of an aromatic hydrocarbon by an olefinic hydrocarbon, in accordance with the present invention, is preferably carried out at a temperature of from about 10 to about 100 C. and under a pressure of from substantially atmospheric to about 100 atmospheres. The particular temperature employed in any given alkylation reaction will depend upon theproperties of the aromatic hydrocarbon undergoing alky ation. In the alkylation zone, it is preferable to have a substantial excess of aromatic hydrocarbons present at all times in order to retard competing side. reaction such aspolymerization of the oleflnic reactants. In general, the molar ratio of aromatic to oleflnic hydrocarbon should be from about 3:1 to about 40:1 or higher; A relatively small amount of hydrogen halide, particularly hydrogen chloride, may be introduced into the alkylation zone in order to promote the activity of the catalyst. Generally, the amount of hydrogen halide present will not exceed more than about 5% by weight of the total hydrocare bon mixture. It is frequently desirable to have hydrogen present generally in a quantity of not more than about 10 mol per cent oithe total hydrocarbons charged.

The following experimental data are introduced in order to illustrate the nature ofsthe results which may be obtained according to the present invention. However, it is not intended that the scope ofthe invention be limited unduly.

EXAMPLE I Table Run Reactants,gms.: Benzine i f'ii'iia" sopropy c o e. gydrogc mchl asses =2:

e um... Final (at room temp.) 'lemp., O Duration, hrs Products gins.

Condensable at -7s=o-. Upper layer Catalyst layer. Hydrogen chlori zana ssfies 5:

-200 Bottoms The experiments were conducted as batch experiments employing a glass lined rotating autoclave of the Ipatief! type. An initial pressure of 30 atmospheres was maintained in each case by the introduction of nitrogen. It will be apparent by comparing runs A and B that the presence of hydrogen chloride resulted in a substantial increase in theproduction of mono-isopropyl benzene as evidenced by the volume per cent of the ISO-175 C. fraction recovered from the reaction products.

Exeuru II A solution was prepared by adding 5 parts by weight of aluminum chloride to 11.3 parts by weight of nitromethane and 82.4 parts by weight of benzene. A homogeneous red solution resulted. A series of catalysts was then prepared by adding 0.05 part by weight of the following alkali and alkaline earth halides to portions of this solution: sodium chloride, potassium chloride, calcium chloride, sodium bromide and potassium bromide. In each case salting out of the catalyst layer occurred. The mixture of catalyst layer and benzene layer was then commingled with isopropyl chloride and the entire mixture was agitated in each case at room temperature and atmospheric pressure. Substantial yields of isopropyl benzene were obtained with each catalyst.

I claim as my invention:

1. An alkylation process which comprises reacting an aromatic hydrocarbon with an alkylating agent under alkylating conditions in intimate contact with a solution of an aluminum halide catalyst in a nitroparafiin and containing a relatively inert salt selected from the group consisting of the alkali and alkaline earth metal chlorides and bromides, said salt being in suificient amount to render the catalyst solution immiscible with said aromatic hydrocarbon, thereafter separating the reaction mixture by stratification into a hydrocarbon layer and'a catalyst layer comprising said solution, and recycling at least a portion of said catalyst layer to the alkylating step.

'2. 'An alkylation process which comprises reacting an aromatic hydrocarbon with an olefinic hydrocarbon under alkylating conditions in intimate contact with a solution of an aluminum chloride catalyst in a nitroparafiln and contain-- ing a relatively inert salt selected from the group consisting of the alkali and alkaline earth metal chlorides and bromides, said salt being in sufficient amount to render the catalyst solution immiscible with said aromatic hydrocarbon, thereafter separating the reaction mixture by stratification into a hydrocarbon layer and a catalyst layer comprising said solution, and recyclinz at least a portion of said catalyst layer to the alkylating-lstep.

3. The process as defined in claim 2 further characterized in that said salt is sodium chloride.

4.,I'he process as defined in claim 2 further characterized in that said nitroparaflln is nitromethane.

5. The process as defined in claim 2 further characterized in that said aromatic hydrocarbon is benzene.

LOUIS SCHMERHNG. 

